Electron tubes of the traveling wave type



Oct. 4, 1955 R. w. PETER ELECTRON TUBES OF' THE TRAVELING WAVE TYPE Filed Sept. 14, 1949 3nventor RDL? W. PETER 2,719,936 Patented Oct. 4, 1955 ELECTRON TUBES OF THE TRAVELING WAVE TYPE Rolf W. Peter, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 14, 1949, Serial No. 115,673

11 Claims. (Cl. S15-3.5)

This invention relates to electron tubes and circuits, and more particularly, to traveling or growing-wave tubes primarily adapted for use as ampliers at very high frequencies.

In a conventional traveling-wave tube an electromagnetic signal wave is coupled to one end of an elongated metal helix of such diameter and pitch that the axial velocity of the wave along the helix is reduced to a fraction, say one-tenth, of the velocity of light, and an electron beam of uniform velocity distribution is projected along the helix, either inside or outside, at a velocity approximately equal to the axial wave velocity. Under such conditions, the electron beam and the wave traveling on the helix interact to cause the amplitude of the wave to increase exponentially, and hence, produce amplication of the signal wave at the output end of the helix. Instead of a metal helix, the wave-guiding means of the tube may be a loaded wave-guide, folded waveguide, baille-loaded coaxial line, waveguide partly lled with dielectric, or other structure capable of reducing the axial velocity of the wave to practical electron velocities.

A growing wave amplifier tube has been proposed by C. W. Hansell, in a co-pending application, Serial No. 83,697, led March 26, 1949, and assigned to the same assignee as the instant application, now Patent No. 2,684,453, granted July 20, 1954, in which the helix of the conventional traveling wave tube described above is replaced by a second electron beam projected along the conventional beam. The two beams are shielded from external electric fields by a conductive shield, The two beams are given slightly different initial direct-current velocities, and the signal to be amplified is applied to either or both beams by suitable modulating means. As the electrical disturbance or wave produced by the modulating means travels along the beams, its amplitude grows exponentially, due to space-charge interaction between f the beams, in a manner somewhat analogous to the phenomena occurring in the conventional traveling wave tube. The diierence in initial direct-current energy of the two beams is converted into additional alternating current or signal energy. The amplified signal energy is then extracted from the beams by suitable means, such as a short helix or a cavity resonator inductively coupled to the beams ahead of the collector.

In accordance with my invention, the basic features of the single-beam traveling-wave tube and the double-beam growing wave tube described are combined in a single amplifier tube. This is accomplished by providing a conventional traveling-wave tube with two separate beams having different initial velocities or a single electron beam having non-uniform velocity distribution.

The principal object of my invention is, therefore, to provide an improved electron tube of the traveling or growing wave type.

This and other objects and advantages of my invention will be apparent from the following detailed description taken in connection with the annexed drawing, in which:

Fig. l is a longitudinal section view, partly schematic, of an electron tube made according to my invention;

Fig. 2 is a transverse section view taken on the line 2 2 of Fig. 1 between the cathodes and the grids;

Fig. 3 is a transverse section view taken on the line 3 3 of Fig. l; and

Fig. 4 is a schematic diagram of a circuit for the tube of Figs. 1-3.

Referring to the drawing, in which the same numerals Vindicate identical parts in the various views, my improved tube comprises an elongated insulating envelope 1 having an enlarged portion 1 at one end thereof. Positioned Within the envelope and extending along the major portion thereof is a continuous wave-guiding means in the form of a wire helix 3. As shown in the drawing, the' diameter and pitch of the helix are substantially constant along the length of the helix and determine a substantially constant axial wave velocity which is a fraction of the velocity of light, as in a conventional traveling wave tube. One end of the helix 3 is connected to a transition 5 consisting of a metal tube of the same diameter as the helix and formed with a slot 5 which varies in pitch from an axial portion of iniinite pitch at the free end to the pitch of the helix 3 at the end connected to the helix.

An input waveguide 7, having an aperture 7 near the closed end 7 thereof to receive the envelope 1 therethrough, is provided opposite the straight portion of the slot 5' for exciting a traveling wave on the transition 5 and helix 3 in accordance with a signal to be amplified. A quarter-wave lange 9 cooperates with the free end of the transition 5 to provide a low impedance, high freqnency connection between the waveguide 7 and transition 5. A tubular metal shield 11 extends from the waveguide over the helix 3 and envelope 1 to a point beyond the end of the envelope.

In accordance with my invention, means are provided adjacent to the helix 3 for projecting two electron beams of different velocity nearly equal to the helix wave velocity through the interior of the helix 3. Such beam projecting means are illustrated in the drawing, for example, as a pair of concentric annular cathodes 13 and 15 and a pair of concentric control grids 16 and 17 for regulating the current density from the two cathodes. The two cathodes and the two grids may be arranged to lie in two concentric spherical surfaces concave toward the helix 3, as shown in Fig. 1. The cathodes 13 and 15 and grids 16 and 17 are separately mounted within the enlarged portion 1 of the envelope 1, in alignment with the helix 3, by means of supporting rods 19 and Z0 and insulating beads 21 secured to terminals 23 extending through the press 25. It will be understood that the two cathodes may be heated by conventional heaters (not shown). The terminals 23 provide separate heater current leads and potential leads for the two cathodes 13 and 15 and the two grids 16 and 17.

While the output system of the tube could be of the same type as the input system shown, I have illustrated a coaxial line output. The end of the helix 3 remote from the transition 5 is connected to a transition 27 having a tapered helical slot 27 similar to slot 5 of transition 5 and having a solid portion 27 connected to an axial rod 29 extending through the end of the envelope 1. The rod 29 cooperates with the adjacent projecting end of the shield 11 to form a coaxial output terminal 31. The solid portion 27 serves as a collector for the combined beams. It will be noted that the input waveguide 7 and the output terminal 31 are coupled to opposite ends of the helix 3, independently of the two beams from cathodes 13 and 15.

My novel tube may be operated as an amplifier as indicated, for example, in Fig. 4. As shown, the outer cathode 13 is connected to the negative terminal of an adjustable direct current voltage source E1 whose positive potential is connected to the transition 5 which serves as an accelerating electrode. This source E1, therefore, determines the direct current velocity u1 of the outer electron beam. The inner cathode l5 is biased either positively or negatively with respect to the outer cathode 13 by an adjustable direct current source AE, so that the direct current velocity u2 of the inner electron beam Will be E2=E1 'AE. An adjustable direct current voltage source E3 connected between the outer cathode 13 and grid 16 determines the current density f1 of the outer electron beam. The current density iz of the inner electron beam is determined by an adjustable direct current source E4. By suitable adjustment of the four sources E1, AE, E3 and E4, the velocities and current densities of the two beams can be adjusted to produce optimum gain.

In a co-pending application of L. S. Nergaard, Serial No. 69,634, filed January 7, 1949, and assigned to the same assignee as the instant application, it has been shown that maximum gain in a double-beam growing wave tube of the Hansell type referred to above is produced when i1 iz Vla/2 1723/2 where i1 and i2 are the current densities and V1 and V2 are the accelerating voltages, respectively, of the two beams. By use of diodes of the same spacing, i. e., having the same perveance per unit area, in the electron gun structure shown in Figs. l and 2, and similar to the gun structure disclosed in said Nergaard application, this relation for maximum gain is automatically satisfied whatever the voltages V1 and V2 are.

It will be understood that the dimensions of the helix or other wave-guiding means used may be varied along the beam axis to obtain optimum synchronism between the velocities of the beams and the traveling wave.

While I have indicated the preferred embodiments of my invention of which I am now aware and have indicated only one specilic application for which the invention may be employed, it will be apparent that my invention is by no means limited to the exact form illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

I claim:

l. A traveling wave electron tube comprising a continuous elongated wave-guiding structure adapted to transmit traveling waves therealong at an axial wave velocity substantially less than the velocity of light, means for projecting a plurality of electron beams of different Velocity nearly equal to said wave velocity along said structure for interaction with Waves thereon, means coupled to said wave-guiding structure independently of said beams for introducing signal waves thereto, and means coupled to said wave-guiding structure independently of said beams for extracting amplified signal energy from said structure.

2. A traveling wave electron tube comprising a continuous elongated wave-guiding structure adapted to transmit traveling waves therealong at a substantially constant predetermined axial velocity substantially less than the velocity of light, means for exciting traveling waves along said structure in accordance with an electrical signal, means adjacent to said structure for projecting a plurality of electron beams of dilferent velocity nearly equal to said predetermined velocity along said structure for interaction with said waves, said means for exciting waves being coupled to said structure independently of said beams, and means coupled to said structure independently of said beams for extracting amplified signal energy from said structure.

3. A traveling wave electron tube comprising means for generating a plurality of electron beams of dilerent velocity along paths extending in the same general direction, a collector positioned in the paths of said beams, a continuous elongated wave-guiding structure adapted to transmit traveling waves therealong at a substantially constant predetermined axial velocity substantially less than the velocity of light positioned adjacent to and between said beam generating means and said collector and extending along said paths, the diierent velocities of said beams being nearly equal to said predetermined wave velocity, means coupled to said structure independently of said beams for exciting traveling waves along said wave-guiding structure in accordance with an electrical signal, and means coupled to said structure independently of said beams for extracting amplified signal energy from said structure.

4. A traveling wave amplifier tube comprising a continuous elongated Wave-guiding structure adapted to transmit traveling waves therealong at a substantially constant predetermined axial velocity substantially less than the Velocity of light, an input transmission line coupled to said structure to excite traveling waves thereon in accordance with a signal, means adjacent to said structure for projecting a plurality of electron beams of different velocity nearly equal to said predetermined velocity along said structure for interaction with said Waves, said input transmission line being coupled to said structure independently of said beams, and an output transmisison line coupled to said structure independently of said beams for extracting amplified signal energy from said structure.

5. A traveling Wave electron tube comprising a continuous elongated wave-guiding structure adapted to transmit traveling waves therealong at a substantially constant axial velocity which is a fraction of the velocity of light, means coupled to one end of said one end of said structure for projecting a plurality of electron beams of different velocities nearly equal to the wave velocity along said structure for interaction with the electric ields produced by said signal waves said means for introducing waves being coupled to said structure independently of said beams, and means adjacent to the opposite end of said structure and coupled thereto independently of said beams for extracting amplified signal energy from said structure.

6. A traveling wave electron tube comprising a continuous elongated helix having substantially constant diameter and pitch along the length thereof, thereby determining a substantially constant axial wave velocity therealong, means for exciting traveling waves along said helix in accordance with an electrical signal, means adjacent said helix for projecting a plurality of electron beams of different velocity nearly equal to said wave velocity along said helix for interaction with said waves, said first-named means being coupled to said helix independently of said beams, and means coupled to said helix independently of said beams for extracting amplified signal energy from said helix.

7. A traveling wave electron tube comprising a continuous elongated electrically conducting helix adapted i. to transmit electromagnetic waves therealong at a substantially constant axial velocity which is a fraction of the velocity of light, means coupled to one end of said helix for introducing traveling signal waves thereto, means adjacent said one end of said helix for projecting a pair of electron beams of different velocity nearly equal to the wave velocity and along said helix for interaction with the electric fields produced by said signal waves, said iirst-named means being coupled to said helix independently of said beams, and means adjacent to the opposite end of said helix and coupled thereto independently of said beams for extracting amplified signal energy from said helix.

8. A traveling wave electron tube including an elongated envelope containing a continuous elongated metal helix having substantially constant diameter and pitch along the length thereof extending along the major portion of said envelope, an electron gun structure mounted adjacent one end of said helix for projecting a pair of electron beams through said helix, said gun structure including a pair of cathodes aligned with said helix and a pair of control grids respectively positioned between said cathodes and said helix, leads extending through said envelope supporting and providing separate potential leads for said cathodes and grids, a beam collector positioned adjacent the end of said helix opposite from said gun structure and a transition element electrically connecting said last-named end of said helix to said beam collector.

9. An electron tube according to claim 8, wherein each of said pairs of cathodes and grids constitutes concentric elements coaxial with said helix.

l0. An electron tube according to claim 8, wherein said cathodes and said grids lie in two concentric spherical surfaces concave toward said helix.

l1. An electron tube according to claim 8, further including a wave guide coupled to said one end of said helix, a conducting shield surrounding said envelope in spaced relation and extending from said wave guide to a point beyond the other end of said helix, and a terminal rod coupled to said collector and extending through said envelope to form with said shield a coaxial terminal for said tube.

References Cited in the le of this patent UNITED STATES PATENTS 2,300,052 Lindenblad Oct. 27, 1942 2,406,370 Hansen et al. Aug. 27, 1946 2,516,944 Barnett Aug. 1, 1950 2,541,843 Tiley Feb. 13, 1951 2,575,383 Field Nov. 20, 1951 2,578,434 Lindenblad Dec. 11, 1951 2,585,582 Pierce Feb. 12, 1952 2,602,148 Pierce July l, 1952 2,652,513 Hollenberg Sept. 15, 1953 OTHER REFERENCES Article by Haeff, Proc. I. R. E., January 1949, pp. 4-10, inclusive.

Article by Hollenberg, Bell System Tech. Jour., Jan- .uary 1949, pp. 52-58, inclusive. 

